An endoscope is a minimal invasive imaging instrument having a rigid or flexible long narrow tube shape, allowing viewing an internal structure of a body through a natural opening or a small incision for clinical inspection and treatment. Typically, endoscopes comprise the lens system, a light and image delivery system such as relay lens or optical fibers, an imaging system, various channels for treatment tool passage, and a display system.
Endoscopic procedures require precise hand-eye coordination and minute manipulation, which can be hardly accomplished by monocular vision. Three-dimensional vision provides more informative and intuitive observation of scene and precise interaction with environment than monocular vision does. Thus, it has become an indispensable element for the endoscope system.
Three-dimensional vision can be accommodated by binocular parallax, motion parallax, confocal scanning, structured light depth extraction techniques, and the like.
U.S. Pat. No. 3,520,587 to Tasaki discloses a stereoscopic endoscope having two objective lens systems with two fiber optic image delivery systems to provide a pair of stereoscopic images. U.S. Pat. No. 5,751,341 to Chaleki and U.S. Pat. No. 5,673,147 to McKinley also disclose systems and methods to provide a pair of stereoscopic images for endoscopes. However, a binocular vision system can cause eye-strain and fatigue for prolonged uses, and requires special eye-wear to see three-dimensional images. Also, it is difficult to design a compact endoscope system without degrading the image quality because the binocular vision system uses multiple camera systems and image delivery systems within the limited space.
U.S. Pat. No. 6,798,570 to Greenberg discloses a three-dimensional imaging and reconstruction system with a single camera system using motion parallax. In this system, the camera system must be continuously moving to generate three-dimensional effect, which can make inspection and treatment procedures complicated and cause trauma to a patient.
U.S. Pat. No. 6,949,069 to Farkas discloses a three dimensional confocal system in which a point of interest is illuminated by a light source using pinhole apertures. The confocal system can provide a high resolution three-dimensional image with a single camera system, but most of illuminating light is wasted and causes noise problem. To overcome this, U.S. Pat. No. 6,749,346 to Dickensheets and U.S. Pat. No. 6,563,105 to Seibel use a single optical fiber to scan and collect reflected light, but point by point scanning can lead to a slow image refresh rate.
U.S. Pat. No. 6,503,195 to Keller discloses a structured light depth extraction system in which a projector projects a structured light pattern such as grids in the visible or invisible form onto an object, and then an image processor calculates the depth information based on the reflected light pattern. In case of using visible light, image quality can be degraded while using invisible light requires an additional sensor system. Also, performance of the structured light depth extraction system depends on the reflectivity of the object.
Conventional endoscope systems usually use a wide field of view; typically, about 70 degree. A wide field of view is useful for viewing an overall internal structure and spotting an area of interest, but it may not provide enough information for diagnosis or treatment because the image produced by the wide field of view tends to suffer from huge distortion and low resolution. A narrow field of view produces a better quality and higher resolution image, and facilitates diagnosis and treatment. A desirable endoscope system must provide both wide and narrow fields of view.
A variable magnification (or a variable field of view) can be accomplished by changing relative locations of lenses in multiple lens system like a zoom lens system. However,it requires complicated macroscopic servo mechanism and yields a slow response time.
Also, conventional endoscope systems have a fixed line of sight along a longitudinal axis of an endoscope body while the area of interest rarely lies on the center thereof. The variable optical axis imaging system without macroscopic reposition or rotation of the endoscope body can benefit a patient by reducing unnecessary contact between lesion and the instrument.
The minimal invasive nature of endoscopic procedures requires the tube with a small diameter to reduce the size of incision and patient's trauma, sharp three-dimensional video images since a clinician can not see an object directly, a wide field of view for surveying the area of interest, a narrow field of view with high resolution images for inspection and treatment, and a variable optical axis to view the surrounding area without macroscopic movements of an endoscope body or parts thereof.